DE10156409A1 - Method for improving smooth running, and corresponding motor, with which air mass flow control includes provision for controlling inlet valve stroke - Google Patents

Abstract

A load controller has two inputs (mLsoll) air mass flow called for by the throttle valve and (hubmin), the minimum inlet valve stroke required to achieve smooth running. It's output values are (EVhubs), the required valve stroke, (aDKsoll) and preferably the control times (stze,stza) for the inlet and outlet valves. The controller checks if the required air mass flow can be set by an inlet valve stroke above the minimum physically possible, otherwise the throttle valve angle is adjusted.

Description

The present invention relates to a method for improving smoothness Multi-cylinder internal combustion engines or internal combustion engines, especially according to Otto Design, with throttle-free load control and a corresponding motor.

The smooth running of such motors is largely dependent on the scatter between the Cylinder generated single moments determined. different Cylinder single torques lead to an uneven concentricity and to vibrations of different ones Frequencies that are not sufficiently canceled out by damping measures in the vehicle alone can be. The result is a significant loss of comfort and an increased Strain on engine components. For this reason - in addition to mechanical Measures - increasingly control engineering approaches developed to the equate individual cylinder moments and thereby improve smoothness.

The individual cylinder torques are essentially a function of the mean indicated internal cylinder pressure pmi that arises in the combustion chamber. The internal cylinder pressure per cylinder pmi is proportional to the fuel mass and the internal efficiency, which is determined by the fuel-air mass ratio. The following applies:

p _mi = n _i . (m _L / m _B. L _st ) .m _B .Hu / V _h

p _mi : internal cylinder pressure
n _i : internal efficiency
m _L : air mass
m _B : fuel mass
L _st : stoichiometric air ratio
H _u : calorific value
V _h : displacement

In conventional gasoline engines with throttled load control, different individual torques in the cylinders result primarily from different fuel masses. This can be caused, for example, by component tolerances of the injection valves. The cylinder-specific air masses usually do not differ in principle due to the complete opening of the inlet valves and the suction against a vacuum that is the same for all cylinders. The cylinder-individual indicated pressures p _mi are therefore primarily proportional to the respective fuel masses, while the influence of the efficiency n _{i, which is} also dependent on the fuel mass, remains secondary. Under these assumptions, comparatively small cylinder torques result from insufficient fuel masses. Conversely, comparatively strong cylinder torques result from excessive fuel masses.

DE 41 22 139 C2 describes a measure for equating the individual moments described on a cylinder-specific adjustment of the injection quantities based. If the cylinder torque is too small, the fuel mass of the is increased corresponding cylinder. Conversely, for too high cylinder torques corresponding reduction of the corresponding injection quantity. The Individual cylinder torques are determined via the smooth running of the engine, which is achieved using the Segment times of a pulse wheel is measured.

In internal combustion engines, especially gasoline engines, with throttle-free load control however, it is also possible that there are differences in moments instead of different ones Amounts of fuel are created by differently measured amounts of air. In this This is no longer the case according to the method described in DE 41 22 139 C2 applicable and even has an adverse effect.

With the same amount of fuel, air mass differences between the cylinders essentially only have an effect on the efficiency n _i . The mean indicated pressures of the cylinders with disproportionately high air mass are higher due to their higher efficiency, which increases their moment. In this case, it is not possible to reduce the torque by reducing the fuel mass, since this would make the mixture, which is already lean due to the excess air, even leaner, which would result in emission disadvantages or the ignition limit being reached.

Conversely, cylinders with too little air mass have a lower one Efficiency and therefore a lower torque than the other cylinders. A Increasing the torque by increasing the fuel mass is due to the danger of Overfatting, which is associated with consumption and emissions disadvantages, is also not possible.

DE 198 59 018 A1 therefore describes a method in which regulation smoothness is achieved through the cylinder-specific metering of fresh air mass. This Metering takes place exclusively via the opening functions of the cargo or Gas exchange valves. A prerequisite for the applicability of this procedure is that the gas exchange valves can be controlled independently of each other. Here too the smoothness rating is determined based on segment times. As an alternative the measurement of the cylinder pressure is proposed.

The method described in DE 41 22 139 C2 for equality of the Cylinder torques are only suitable if the differences between the cylinder torques caused by scatter within the injected fuel quantities were. For throttle-free engines, however, it is as described above was not applicable. The method described in DE 198 59 018 A1 is for Choke-free internal combustion engines can be used, but uses a separate one Possibility to control the gas exchange valves in advance. If a throttle-free Load control is implemented via a global actuator that is based on several Gas exchange valves acting simultaneously, the method according to DE 198 59 018 A1 can no longer be applied. Such a throttle-free load control with a global Actuators are often found in mechanical systems for adjusting the Intake valves.

The present invention has for its object to provide an improved method Increase the smooth running of internal combustion engines with throttle-free load control as well to provide a correspondingly improved engine. This task is accomplished with the Features of the claims solved.

The invention is based on the basic idea that the internal combustion engine in addition to the throttle-free load control elements, a device for Generation of a variable intake manifold vacuum. Internal combustion engines with throttle-free load control is controlled without throttle, with the intake manifold pressure almost corresponds to the ambient pressure. The generation of a variable intake manifold vacuum is provided in such internal combustion engines at best for reasons of emergency operation, for example around the internal combustion engines throttled in a conventional one if necessary Mode to operate. In part, the throttle device is also used to im Collector a slight negative pressure, for example for the tank ventilation produce. In these cases, throttle-free load control is usually still used spoken, since the air metering takes place essentially via the inlet valves.

The present invention will hereinafter be described with reference to a preferred one Embodiment described with reference to the drawings. Show it:

Figure 1 is a schematic cross section through a structure of an internal combustion engine according to the present invention.

Fig. 2 is a block diagram of the load control according to the present invention;

Fig. 3 _is an exemplary relationship between the smoothness actual value Lr and the minimum lift hub _min; and

Fig. 4 is a block diagram for a control loop of the method according to the invention and the internal combustion engine according to the invention.

The following statements refer to the representation in Fig. 1 to internal combustion engines or internal combustion engines, in which the throttle-free load control via intake valves with a mechanically adjustable, variable valve lift connected with a mechanical device for adjusting the intake camshaft spread. In principle, however, the invention can also be applied to other systems, for example with electrically or hydraulically operated inlet valves. A throttle valve is preferably used as the actuator for the variable intake manifold vacuum.

Component tolerances in the valve control can lead to the individual Different air volumes are supplied to cylinders. The following is an example assumed that the component tolerances essentially only on the strokes of the intake valves and that the relative tolerances increase with increasing strokes get smaller. The influence of the component tolerances is usually the greater the lower the requested air volume and the smaller the valve strokes to be set are. The different amounts of air in the cylinders lead, as in the state of the Technology shown, to different cylinder single torques and thus to one poor smoothness. A particularly critical operating point is idling when the engine is warm Motor, since the air quantities are very small here.

Accordingly, the invention assumes the different amounts of air Equal cylinders to improve smoothness. This depends on Leave operating point of throttle-free operation. Instead, a mixed operation takes place instead, in which the load control simultaneously via both the intake valves and the throttle valve takes place. By generating an intake manifold vacuum with the Throttle valve reduces the density of the intake air. With the same amount of air then a much larger one, d. H. less tolerant, the intake valve stroke Episode. The decreasing tolerance influence with the larger valve stroke leads to that the desired equality of the cylinder air masses and thus the Individual cylinder torques are reached.

A preferred possibility for the corresponding load control is shown in the block diagram according to FIG. 2. The first input variable is the required air mass flow mL _should , which z. B. is calculated depending on the moment desired by the driver. The second input variable is the lower stroke limitation, ie the minimum required valve stroke strokemin, with the z. B. acceptable running smoothness can be represented. The output variables of the load control are the valve lift EV _{hubs to be set} , the throttle valve angle α _DKsoll and preferably the timing for the intake and exhaust side camshaft adjustment stz _e and stz _a .

In the "load control" block shown in FIG. 2, it is checked whether the air mass flow mL _{to be} set can be set without throttling through the throttle valve with a valve lift Evhubs which is above the minimum stroke value hubmin. If this is the case, unrestricted operation continues to take place. May, however, _should mL hubmin due to the lower stroke limit is not reached, so there is an increase in intake manifold vacuum through the throttle valve by a corresponding control signal for the throttle position α _DKsoll and the timing stz _e and _a stz is determined.

According to one embodiment of the invention, the lower stroke limit is hubmin regardless of the operating point, d. H. similar to a (virtual) mechanical Stop setting.

In a further embodiment, the value of the lower stroke limit becomes hubmin and the associated throttling depending on the operating point of the Internal combustion engine piloted, e.g. B. depending on the engine temperature and / or Engine speed and / or the idle detection and / or from the past time Start end.

In a further embodiment, the lower stroke limitation is in the stroke Motor control not only pre-controlled, but online depending on the prevailing one The engine runs smoothly. With such an adaptive method it is possible automatically throttle only those engines that have a bad one Have smooth running. In this way, there is a possible consumption disadvantage, which is characterized by the stroke limitation and throttling could result to a minimum necessary Dimension reduced.

The predominant smoothness of the engine can be controlled by the engine for example from the time intervals between the successive ignitions, the so-called segment times can be determined. The segment times are recorded for example via a segment wheel attached to the crankshaft in connection with a crankshaft angle sensor arranged on the crankcase. From the Segment times, the actual running smoothness value Lrist is determined in the control. An exemplary The calculation rule is, based on the segment times, the individual cylinder first To calculate acceleration values. A global smooth running actual value Lrist is then for example the maximum - based on the last two engine revolutions absolute distance between two acceleration values measured in order of ignition. Alternatively, there are of course other calculation rules for the smooth running actual value Lrist conceivable, e.g. B. Amounts, averages, standard deviations. An alternative Possibility of determining smooth running could be based on the measurement of the cylinder internal pressures based.

The invention is based in particular on the assumption that with increasing lower stroke limits and thus with a greater throttling the smoothness improves and that this smoothness improvement is reflected in the smoothness actual value Lrist. This assumption has proven to be valid in experiments as long as the stroke limitation is adjusted in a travel range in which a throttle-free air metering is possible at all in idle or in the part load range close to idle. Fig. 3 shows an example of a typical relationship between Lrist and the set lower stroke limit hubmin.

The adaptation method according to the invention can be implemented, for example, as a control loop, as is shown schematically in FIG. 4. The smoothness actual Lrist is thereby _intended to an applicable target value Lr regulated. The input variable of the controller is therefore the smooth running actual value Lrist, the output variable is the minimum stroke strokemin. If the smooth running actual value Lrist results in poor smoothness in relation to the smooth running setpoint Lr _should , the controller increases the minimum stroke strokemin. Conversely, if the running smoothness Lrist is "too good", the value of hubmin is reduced until Lr target _is reached. In the case of internal combustion engines for which the smooth running actual value Lrist is equal to or better than the smooth running setpoint Lr _{should in the} unthrottled state, the lower stroke limitation strokemin is reduced to such an extent that the throttle-free state is set or maintained. In this case, a lower stop prevents the controller output "running away" downwards. On the other hand, an upper stop of the controller output prevents "running away" from the hubmin upwards if the internal combustion engine has very large component tolerances and the smoothness setpoint Lr _is not _to be reached.

A monitoring level for the adaptation method according to the invention can if necessary, ensure the functional reliability of the controller and implausible Recognize route behavior. A controller release can depend on the controller, for example from the operating point, from the engine temperature, from the idling state, from the Engine speed, the vehicle speed, a fault condition of the overall system activate.

Instead of the control loop described, an optimization method can also be used be used, which is always the optimal lower one for each operating point Stroke limitation strokemin determined with regard to the achievable smoothness.

Combinations of the described embodiments are of course also possible possible. For example, the adaptive lower stroke limit can be connected to the Throttling can only be activated in the warm operating state while the Internal combustion engine is operated without throttling during warm-up.

Under certain conditions are, in addition to the described Air mass equality, also measures to adjust the individual cylinder Injection times can be used, e.g. B. to adjust an emission-optimal mixture. A an additional possibility of intervention is an adjustment of the cylinder-specific ignition angle. These measures can be carried out using the method according to the invention can of course be easily combined.

The invention can be compared to known systems and methods achieve significant advantages such. B. a significant improvement in smoothness of Internal combustion engines with throttle-free load control, a gain in comfort and lower Component stress due to lower vibrations in the vehicle and a possibility for Compensation of manufacturing or aging-related component tolerances in the intake valve Adjustment. In addition, in particular in the embodiment with adaptive Stroke limitation ensures smooth running over the running time of the internal combustion engine guaranteed. Another major advantage is that the consumption potential (Fuel consumption) in throttle-free operated internal combustion engines due to low component tolerances do not require throttling measures, not impaired becomes.

Claims (22)

1. Internal combustion engine with throttle-free load control and a device for Generation of a variable intake manifold vacuum with the throttle-free Load control cooperates to at least temporarily the internal combustion engine in one To operate in mixed operation. 2. Internal combustion engine according to claim 1, wherein the means for generating a variable intake manifold vacuum is a throttle valve. 3. Internal combustion engine according to claim 1 or 2, wherein the throttle-free Load control has inlet valves with variably adjustable valve lift. 4. Internal combustion engine according to claim 3, wherein the valve lift is mechanically adjustable is. 5. Internal combustion engine according to claim 3 or 4, wherein the throttle-free Load control with a, preferably mechanical, device for adjusting the Inlet camshaft spread is coupled. 6. Internal combustion engine according to one of claims 1 to 5 with a Control device which, depending on the operating point of the internal combustion engine between switches to operation with throttle-free load control and mixed operation. 7. Internal combustion engine according to claim 6, wherein the control device in Mixed operation causes a load control via the intake valves and the throttle valve. 8. Internal combustion engine according to claim 6 or 7, wherein the control means _{is intended} as inputs a requested air mass flow m and a minimum valve hubmin and as outputs an adjusted valve EV _hubs, an adjusted throttle angle α _Dksoll and timing stz _e and stz _a for the inlet and has exhaust-side camshaft adjustment. 9. Internal combustion engine according to one of claims 6 to 8, wherein the control device is part of a control circuit which is _intended as an input variable a smooth running setpoint Lr and a determined smooth running actual value Lrist of the internal combustion engine and as an output variable has the minimum valve lift hubmin, which the control device together with the required air mass flow mL _{should be} supplied. 10. Method for operating an internal combustion engine with a throttle-free Load control, with an intake manifold vacuum depending on operating conditions is varied to the internal combustion engine at least temporarily in a mixed operation to operate. 11. The method of claim 10, wherein varying the intake manifold vacuum by there is a throttle valve. 12. The method of claim 10 or 11, wherein the throttle-free load control by Intake valves with variably adjustable valve lift. 13. The method of claim 12, wherein the valve lift is mechanically adjusted. 14. The method according to claim 12 or 13, wherein the throttle-free load control with one, preferably mechanical, device for adjusting the Inlet camshaft spread is coupled. 15. The method according to any one of claims 10 to 14, wherein depending on Operating point of the internal combustion engine to switch between operation with throttle-free load control and mixed operation. 16. The method of claim 15, wherein in mixed operation, a load control over the Intake valves and the throttle valve is done. 17. The method according to any one of claims 10 to 16, wherein to assess whether a mixed operation is required, a required air mass flow mL _{should be used} as input variables and a minimum valve lift hubmin and as output variables a valve lift EV _{hubs to be set} , a throttle valve angle α _Dksoll and Control times stz _e and stz _a are generated for the intake and exhaust-side camshaft adjustment. 18. The method according to claim 17, wherein it is checked on the basis of the input variables whether the required air mass flow mL _{should be} adjustable without leaving the throttle-free load control with a valve lift Evhubs that is above the minimum valve lift hubmin. 19. The method according to any one of claims 10 to 18, wherein when leaving the throttle-free load control is required, the intake manifold vacuum is increased. 20. The method of claim 19, wherein when increasing the intake manifold _vacuum corresponding values for the throttle valve position α _Dksoll and _timing stz _e and stz _a are generated for the intake and exhaust side camshaft adjustment. 21. The method according to any one of claims 10 to 20, wherein for the load control or several operating conditions such as engine temperature, engine speed, Idle detection and / or elapsed time since the start is taken into account. 22. The method according to any one of claims 10 to 21, wherein the considered for load control operating condition comprises the running smoothness of the internal combustion engine, which is controlled by a control circuit whose input a Laufruhe- setpoint Lr _to and whose output is a minimum valve lift is hubmin.